U.S. patent application number 14/853311 was filed with the patent office on 2016-03-17 for light emitting device including light emitting element with phosphor.
This patent application is currently assigned to NICHIA CORPORATION. The applicant listed for this patent is NICHIA CORPORATION. Invention is credited to Atsushi BANDO, Shoji HOSOKAWA, Daiki KURAMOTO, Kenji NAKATA.
Application Number | 20160079484 14/853311 |
Document ID | / |
Family ID | 55455628 |
Filed Date | 2016-03-17 |
United States Patent
Application |
20160079484 |
Kind Code |
A1 |
HOSOKAWA; Shoji ; et
al. |
March 17, 2016 |
LIGHT EMITTING DEVICE INCLUDING LIGHT EMITTING ELEMENT WITH
PHOSPHOR
Abstract
A light emitting device includes a light emitting element, a
molded member, and a sealing member. The light emitting element is
arranged on or above the molded member. The sealing member covers
the light emitting element. The sealing member contains a phosphor,
and a filler material. The phosphor can be excited by light of the
light emitting element, and emit luminescent radiation. The filler
material contains neodymium hydroxide, neodymium aluminate or
neodymium silicate. The filler material absorbs a part of the
spectrum of the mixed light of the light emitting element and the
phosphor so that the other parts of the spectrum of this mixed
light are extracted from the light emitting device.
Inventors: |
HOSOKAWA; Shoji;
(Tokushima-shi, JP) ; KURAMOTO; Daiki; (Anan-shi,
JP) ; NAKATA; Kenji; (Anan-shi, JP) ; BANDO;
Atsushi; (Itano-gun, JP) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
NICHIA CORPORATION |
Anan-shi |
|
JP |
|
|
Assignee: |
NICHIA CORPORATION
Anan-shi
JP
|
Family ID: |
55455628 |
Appl. No.: |
14/853311 |
Filed: |
September 14, 2015 |
Current U.S.
Class: |
257/98 |
Current CPC
Class: |
H01L 23/29 20130101;
H01L 2924/181 20130101; H01L 33/52 20130101; H01L 33/501 20130101;
H01L 33/56 20130101; H01L 2924/01015 20130101; H01L 23/295
20130101; H01L 33/502 20130101; H01L 31/0203 20130101; H01L 21/56
20130101; H01L 2924/0106 20130101; H01L 33/508 20130101; H01L
2924/186 20130101 |
International
Class: |
H01L 33/50 20060101
H01L033/50; H01L 33/52 20060101 H01L033/52 |
Foreign Application Data
Date |
Code |
Application Number |
Sep 16, 2014 |
JP |
2014-188268 |
Claims
1. A light emitting device comprising: a light emitting element; a
molded member that holds said light emitting element; and a sealing
member that covers said light emitting element, the sealing member
containing a phosphor that can be excited by light of said light
emitting element and emit luminescent radiation, and a filler
material that contains neodymium hydroxide, neodymium aluminate or
neodymium silicate.
2. The light emitting device according to claim 1, wherein said
filler material contains neodymium hydroxide, wherein the neodymium
hydroxide is Nd(OH).sub.3 or NdO.sub.2H.
3. The light emitting device according to claim 1, wherein said
filler material contains neodymium aluminate or neodymium silicate,
wherein the neodymium aluminate or neodymium silicate is
represented by a general formula Nd.sub.xM.sub.yO.sub.z where M is
Si or Al, and x, y and z satisfy 1.ltoreq.x.ltoreq.10,
1.ltoreq.y.ltoreq.15, and 3.ltoreq.z.ltoreq.45, respectively.
4. The light emitting device according to claim 1, wherein said
filler material contains neodymium aluminate or neodymium silicate,
wherein the neodymium aluminate or neodymium silicate is at least
one selected from the group consisting of NdAlO.sub.3,
Nd.sub.2Si.sub.2O.sub.7, and Nd.sub.9.83((Si,
Al)O.sub.4).sub.6O.sub.2.
5. The light emitting device according to claim 1, wherein the
reflectance of said filler material is not smaller than 50% and not
greater than 65% in the wavelength range of not shorter than 575 nm
and not longer than 605 nm.
6. The light emitting device according to claim 1, wherein the
added amount of said filler material is not smaller than 0.01% by
weight and not greater than 10% by weight of the material of said
sealing member.
7. The light emitting device according to claim 1, wherein the mean
particle diameter of said filler material is not smaller than 0.1
.mu.m and not greater than 5 .mu.m.
8. The light emitting device according to claim 1, wherein said
phosphor contains at least one selected from the group consisting
of (Lu, Y, Gd).sub.3(Al, Ga).sub.5O.sub.12:Ce, (Sr,
Ca)AlSiN.sub.3:Eu, (Ba, Sr, Ca).sub.2SiO.sub.4:Eu,
Ca.sub.8MgSi.sub.4O.sub.16Cl.sub.2:Eu, and
Sr.sub.4Al.sub.14O.sub.25:Eu.
9. The light emitting device according to claim 1, wherein said
sealing member includes a first portion that covers said light
emitting element and contains said phosphor, and a second portion
that covers said first portion and contains said filler
material.
10. The light emitting device according to claim 9, wherein said
first portion is spaced at an interval away from said second
portion.
11. The light emitting device according to claim 9, wherein said
first or second portion is arranged on the upper surface of said
molded member.
12. The light emitting device according to claim 1, wherein said
phosphor and said filler material are mixed in said sealing
member.
13. The light emitting device according to claim 1, wherein the
material of the said sealing member is a light-transmissive resin.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] The present application claims priority under 35 U.S.C.
.sctn.119 to Japanese Patent Application No. 2014-188,268, filed
Sep. 16, 2014. The contents of this application are incorporated
herein by reference in their entirety.
BACKGROUND OF THE INVENTION
[0002] 1. Field of the Invention
[0003] The present disclosure relates to a light emitting device
that includes a light emitting element with a phosphor.
[0004] 2. Description of the Related Art
[0005] In recent years, light emitting diodes (hereinafter also
referred to as LEDs), which provide substantial energy savings, are
widely used as light emitting elements instead of filament lamps.
Also, light emitting devices are known which include a light
emitting element that is formed of gallium nitride (GaN), and a
yellow phosphor, for example.
[0006] In ordinary lighting fields, a high color rendering is
desirable. For example, Japanese Patent Laid-Open Publication No.
JP 2004-193,581 A1 discloses a light emitting device that includes
a member formed of resin, or the like, mixed with neodymium oxide
(Nd.sub.2O.sub.3) particles. According to this publication, its
color rendering index Ra can be increased since light in a specific
wavelength range is absorbed. In addition, International
Publication No. WO 2011-142,127 A1 discloses a light emitting
device that includes glass containing neodymium ions (Nd.sup.3+).
According to this publication, its color rendering index as well as
its luminous efficacy can be improved.
[0007] Neodymium oxide and glass containing neodymium absorb light
in specific wavelength ranges. Correspondingly, the entire light
emission efficiencies of the light emitting devices will be reduced
by the absorbed light. From this viewpoint, a light emitting device
is desired which has a high color rendering while suppressing the
reduction of its light emission efficiency.
[0008] The present invention is devised for further improvements.
It is one object of the present invention to provide a light
emitting device that has both a high color rendering and an
improved light emission efficiency.
SUMMARY OF THE INVENTION
[0009] A light emitting device according to one aspect of the
present invention includes a light emitting element, a molded
member, and a sealing member. The light emitting element is
arranged on or above the molded member. The sealing member covers
the light emitting element. The sealing member contains a phosphor,
and a filler material. The phosphor can be excited by light of the
light emitting element, and emit luminescent radiation.
[0010] The filler material contains neodymium hydroxide, neodymium
aluminate or neodymium silicate.
[0011] According to the above aspect, not only the color rendering
but also the light emission efficiency of the light emitting device
can be high.
BRIEF DESCRIPTION OF THE DRAWINGS
[0012] A more complete appreciation of the invention and many of
the attendant advantages thereof will be readily obtained as the
same becomes better understood by reference to the following
detailed description when considered in connection with the
accompanying drawings, wherein:
[0013] FIG. 1 is a schematic plan view showing a light emitting
device according to an embodiment of the present invention;
[0014] FIG. 2 is a schematic cross-sectional view of the light
emitting device shown in FIG. 1 taken along the line II-II;
[0015] FIG. 3 is a schematic cross-sectional view showing a light
emitting device according to a first modified embodiment of the
present invention;
[0016] FIG. 4 is a schematic cross-sectional view showing a light
emitting device according to a second modified embodiment of the
present invention;
[0017] FIG. 5 is a schematic cross-sectional view showing a light
emitting device according to a third modified embodiment of the
present invention;
[0018] FIG. 6 is a schematic cross-sectional view showing a light
emitting device according to a fourth modified embodiment of the
present invention;
[0019] FIG. 7 is a schematic cross-sectional view showing a light
emitting device according to a fifth modified embodiment of the
present invention;
[0020] FIG. 8 is a graph showing the reflection spectra of filler
materials used in an example 1 and a comparative example;
[0021] FIG. 9 is a graph showing the reflection spectra of filler
materials used in an example 2 and the comparative example;
[0022] FIG. 10 is a graph showing the reflection spectra of filler
materials used in an example 3 and the comparative example;
[0023] FIG. 11 is a graph showing the reflection spectra of filler
materials used in an example 4 and the comparative example;
[0024] FIG. 12 is a graph showing the light emission spectra of
light emitting devices according to the example 1 and the
comparative example;
[0025] FIG. 13 is a graph showing the light emission spectra of
light emitting devices according to the example 2 and the
comparative example;
[0026] FIG. 14 is a graph showing the light emission spectra of
light emitting devices according to the example 3 and the
comparative example; and
[0027] FIG. 15 is a graph showing the light emission spectra of
light emitting devices according to the example 4 and the
comparative example.
DESCRIPTION OF EMBODIMENTS
[0028] The embodiments will now be described with reference to the
accompanying drawings, wherein like reference numerals designate
corresponding or identical elements throughout the various
drawings.
[0029] It should be appreciated, however, that the embodiments
described below are illustrations of a light emitting device to
give a concrete form to technical ideas of the invention, and a
light emitting device of the invention is not specifically limited
to description below. Furthermore, it should be appreciated that
the members shown in claims attached hereto are not specifically
limited to members in the embodiments. Unless otherwise specified,
any dimensions, materials, shapes and relative arrangements of the
parts described in the embodiments are given as an example and not
as a limitation. Additionally, the sizes and the positional
relationships of the members in each of drawings are occasionally
shown exaggeratingly for ease of explanation.
[0030] In description of the present invention, relationship
between color name and chromaticity coordinates, relationship
between light wavelength range and monochromatic light, and the
like are based on the JIS standard (JIS Z8110). Specifically, a
range of 380 to 455 nm corresponds to the bluish violet color, a
range of 455 to 485 nm corresponds to blue, a range of 485 to 495
nm corresponds to bluish green, a range of 495 to 548 nm
corresponds to green, a range of 548 to 573 nm corresponds to
yellowish green, a range of 573 to 584 nm corresponds to yellow, a
range of 584 to 610 nm corresponds to apricot, and a range of 610
to 780 nm corresponds to red.
[0031] A light emitting device according to an embodiment includes
a light emitting element, a molded member that holds the light
emitting element, and a sealing member that covers the light
emitting element. The sealing member contains a phosphor, and a
filler material. The phosphor can be excited by light of the light
emitting element, and emit luminescent radiation. The filler
material absorbs a part of the spectrum of the mixed light of the
light emitting element and the phosphor, and reflects the other
parts of the spectrum of this mixed light. Since a part of the
spectrum of the mixed light of the light emitting element and the
phosphor is absorbed, the profile of the spectrum of the mixed
light correspondingly drops. Thus, the color rendering of the light
emitting device can be improved. On the other hand, the reflected
light by the filler material is extracted as light emitted by the
light emitting device. In order to improve the light emission
efficiency of the light emitting device according to the present
invention as compared with the light emitting devices discussed in
the background, it is necessary to increase the reflected light. To
achieve this, the filler material of the embodiment contains
neodymium hydroxide, neodymium aluminate, or neodymium silicate.
These materials have higher reflectance in a specific wavelength
range than neodymium oxide and neodymium glass discussed in the
background. Accordingly, the light emitting device of the
embodiment can have a high color rendering while providing a light
emission efficiency higher than the light emitting devices
discussed in the background.
[0032] Various shapes of light emitting devices including a light
emitting element are known such as bullet type and surface mount
type light emitting devices. The bullet type light emitting device
in this specification refers to a light emitting device that
includes a bullet-shaped sealing member for covering a light
emitting element, and leads. The light emitting element is mounted
on one of the leads. The leads serve as terminals to be connected
to the outside. The surface mount type light emitting device refers
to a light emitting device that includes a light emitting element,
a molded member that includes leads and holds the light emitting
element, and a sealing member that is arranged on the molded member
and covers the light emitting element. In addition, another type of
light emitting device is known which includes a light emitting
element, a plate-shaped circuit board on which the light emitting
element is mounted, and a sealing member that contains a phosphor
and is formed in a lens shape, or the like.
[0033] FIG. 1 is a schematic plan view showing a light emitting
device according to the embodiment of the present invention. FIG. 2
is a schematic cross-sectional view of the light emitting device
shown in FIG. 1 taken along the line II-II indicated in FIG. 1. The
light emitting device according to the embodiment is an exemplary
surface mount type light emitting device.
[0034] The light emitting device 100 includes a light emitting
element 10 which is formed of gallium-nitride-based semiconductors
and emits light in the short wavelength range of visible light, and
a molded member 40 which has a recessed part for accommodating the
light emitting element 10. The molded member 40 includes first and
second leads 20 and 30. Parts of the first and second leads 20 and
30 are exposed from the bottom surface of the recessed part. The
molded member 40 is integrally formed with the leads 20 and 30, and
is formed of a thermoplastic resin or thermosetting resin. The
recessed part of the molded member 40 is surrounded by the bottom
and side surfaces. The light emitting element 10 is arranged on the
bottom surface of the recessed part. The light emitting element 10
includes a pair of electrodes (positive and negative electrodes).
The pair of electrodes (positive and negative electrodes) are
electrically connected to the first and second leads 20 and 30
through wires 60. The light emitting element 10 is enclosed by the
sealing member 50. The sealing member 50 contains a phosphor 70,
and a filler material 80. The phosphor 70 converts light having a
peak wavelength of the light emitting element 10 into light having
a peak wavelength different from the light of the light emitting
element 10. The filler material 80 absorbs a part of the spectrum
of the mixed light of the light emitting element 10 and the
phosphor 70, and reflects the other parts of the spectrum of this
mixed light. The following description will describe the components
of the light emitting device.
[0035] (Filler Material)
[0036] As shown in FIG. 2, the sealing member 50 contains the
phosphor 70 and the filler material 80. In the embodiment shown in
FIG. 2, the phosphor and the filler material 80 are contained in
the common sealing member 50. Specifically, the phosphor and the
filler material are mixed so as to be substantially uniformly
distributed in the sealing member. In this embodiment, in the
production process of the light emitting device, only a step for
mixing the materials of the phosphor, the filler material, and the
sealing member is required for preparation of the sealing member.
For this reason, the workability can be high in the production
process of the light emitting device according to this embodiment
as compared with other modified embodiments which will be described
later.
[0037] In order to efficiently absorb a part of light in the range
from yellow to apricot in the mixed light of the light emitting
element 10 and the phosphor 70, which is excited by the light of
the light emitting element 10, the filler material is arranged in
proximity to the light emitting element 10 and the phosphor 70 in
the sealing member 50. It is preferable that the reflectance of the
filler material is not smaller than 50% and not greater than 65% in
the wavelength range of not shorter than 575 nm and not longer than
605 nm. The reason is that if the reflectance exceeds the upper
limit in the aforementioned wavelength range, the part of light
cannot be sufficiently absorbed. As a result, the color rendering
of the light emitting device may not be high enough. On the other
hand, if the reflectance falls below the lower limit, the absorbed
amount of light by the filler material is too much. This may cause
reduction of the light emission efficiency of the light emitting
device.
[0038] The material of the filler material 80 includes at least
neodymium hydroxide, neodymium aluminate, or neodymium silicate.
The sealing member 50 mixed with particles of this material can be
used. It is preferable that the added amount of neodymium
hydroxide, neodymium aluminate, or neodymium silicate is not
smaller than 0.01% by weight and not greater than 10% by weight of
the material of the sealing member 50. The reason is that if the
added amount of neodymium hydroxide, neodymium aluminate, or
neodymium silicate is too small, the aforementioned part of light
cannot be sufficiently absorbed by the filler material. As a
result, the color rendering of the light emitting device may not be
high enough. On the other hand, if the added amount is too large,
the absorbed amount of light by the filler material is too much.
This may cause reduction of the light emission efficiency of the
light emitting device. Examples of neodymium hydroxide can be
provided by Nd(OH).sub.3, and NdO.sub.2H which can be obtained by
thermal decomposition of Nd(OH).sub.3 (e.g., 390.degree. C. in Pt
crucible). In particular, Nd(OH).sub.3 is preferably used. The
reason is that Nd(OH).sub.3 has a good reflectance in the
aforementioned wavelength range so that the color rendering of the
light emitting device can be sufficiently increased while the light
emission efficiency of the light emitting device can be improved as
compared with other materials. The general formula of neodymium
silicate or neodymium aluminate is represented by
Nd.sub.xM.sub.yO.sub.z. Here, M is Si or Al, and x, y and z satisfy
1.ltoreq.x.ltoreq.10, 1.ltoreq.y.ltoreq.15, and
3.ltoreq.z.ltoreq.45, more preferably 1.ltoreq.x.ltoreq.10,
1.ltoreq.y.ltoreq.10 and 3.ltoreq.z.ltoreq.30, respectively. This
is because neodymium silicate or neodymium aluminate having this
composition for providing a suitable reflectance capable of
achieving the effect according to the present invention can be
relatively easily synthesized, and commercially available.
[0039] Exemplary compositions of such neodymium aluminate or
neodymium silicate can be provided by NdSiO.sub.5,
Nd.sub.2SiO.sub.5, Nd.sub.2Si.sub.2O.sub.7,
Nd.sub.2Si.sub.3O.sub.9, Nd.sub.2Si.sub.3O.sub.12,
Nd.sub.4Si.sub.3O.sub.12, Nd.sub.9.33(SO.sub.4).sub.6O.sub.2,
NdAlO.sub.3, NdAl.sub.11O.sub.8, NdAl.sub.11O.sub.18,
Nd.sub.1.65Al.sub.23.43O.sub.38, and Nd.sub.4Al.sub.2O.sub.9, for
example. In particular, NdAlO.sub.3, Nd.sub.2Si.sub.2O.sub.7, and
Nd.sub.9.83((Si, Al)O.sub.4).sub.6O.sub.2 are preferably used which
have smaller mole ratios of Nd with respect to Al or Si. The reason
is that as the mole ratio of Nd with respect to Al or Si becomes
smaller, the filler material is likely to have a better reflectance
capable of achieving the effect according to the present
invention.
[0040] The mean particle diameter of the filler material is not
smaller than 0.1 .mu.m and not greater than 5 .mu.m. It is
preferable that this mean particle diameter is not smaller than 1
.mu.m and not greater than 5 .mu.m. Furthermore, it is more
preferable that the mean particle diameter of the filler material
is not smaller than 1 .mu.m and not greater than 2 .mu.m. The
reason is that if the mean particle diameter of the filler material
is too small, the aforementioned part of light cannot be
sufficiently absorbed. As a result, the color rendering of the
light emitting device may not be high enough. On the other hand, if
the mean particle diameter of the filler material is too large, the
added amount of the filler material is necessarily increased to
achieve a certain diffusion effect. In the case where the added
amount of the filler material is increased, the absorbed amount of
light by the filler material may be too much. As a result, this may
cause reduction of the light emission efficiency of the light
emitting device. From this viewpoint, it is preferable to avoid
increasing the mean particle diameter of the filler material too
much.
[0041] In this specification, the term "mean particle diameter"
refers to a mean particle diameter measured by an aperture's
electrical resistance method (electrical sensing zone method) based
on the Coulter principle. The aperture's electrical resistance
method is a particle measurement method using electric resistances
of particles. Specifically, the method obtains the diameters of
particles of the phosphor or the filler material in accordance with
their electric resistances produced when they pass an aperture of
an aperture tube after they are distributed in an electrolytic
solution.
[0042] In the embodiment shown in FIG. 2, the phosphor 70 as well
as the filler material 80 is mixed in the sealing member 50. That
is, the phosphor 70 and the filler material 80 can be contained in
the common member. The filler material 80 can be preferably
distributed in a part of the sealing member 50 outside the part
where the phosphor 70 is mainly distributed as shown in FIG. 3
rather than being uniformly distributed together with the phosphor
70 in the sealing member 50. This arrangement can be obtained by
firstly settling the phosphor 70 and then settling the filler
material 80 in the sealing member 50, for example. Alternatively,
the arrangement of the phosphor and the filler material can be
controlled by difference between the settling velocities of the
phosphor and the filler material caused by the difference between
their specific gravities so that the filler material can be located
on or above the phosphor.
[0043] (Light Emitting Element 10)
[0044] The light emitting element 10 can emit light from the
ultraviolet range to the visible light range. The peak wavelength
of light emitted by the light emitting element 10 preferably falls
within the wavelength range from 240 to 520 nm, more preferably
from 420 to 470 nm. For example, a nitride semiconductor device
(In.sub.xAl.sub.yGa.sub.1-x-yN, 0.ltoreq.x, 0.ltoreq.y,
x+y.ltoreq.1) can be used as the light emitting element 10.
[0045] The light emitting element 10 includes semiconductor layers
of nitride semiconductors. The semiconductor layers include n-type,
active, and p-type layers that are deposited in this order on or
above a sapphire substrate. An n-pad electrode is formed on an
exposed part of the n-type semiconductor that extends in a line
which extends in a wafer before the wafer is divided into chips. On
the other hand, a p-pad electrode is formed on a p-ohmic electrode.
The light emitting element 10 preferably includes the active layer
which has a light emission peak wavelength in the range from about
240 to 520 nm and can emit light with a light emission wavelength
capable of efficiently exciting the phosphor substance. Although
the nitride semiconductor light emitting element has been
illustratively described as the light emitting element 10, the
light emitting element according to the present invention is not
limited to this.
[0046] The light emitting element 10 emits light having a light
emission peak wavelength in the aforementioned wavelength range. At
least one phosphor 70 is excited by the light of the light emitting
element 10. As a result, the light emitting device emits
predetermined color light. In addition, this light emitting element
10 can have a narrow width of its light emission spectrum. For this
reason, the light emitting element 10 can efficiently excite the
phosphor.
[0047] (Phosphor 70)
[0048] The phosphor 70 according to this embodiment is distributed
in the sealing member 50. The sealing member 50 serves not only as
a member for protecting the light emitting element 10 and the
phosphor 70 from the external environments but also as a wavelength
conversion member for absorbing a part of the light of the light
emitting element 10 for wavelength conversion. In the case where
the sealing member including the phosphor is arranged in proximity
to the light emitting element 10, the light of the light emitting
element 10 can be efficiently converted into light with a different
wavelength from the light of the light emitting element 10. As a
result, the light emitting device can have a high light emission
efficiency. However, the sealing member 50 including the phosphor
70 is not limited to be arranged in proximity to the light emitting
element 10. In consideration of influence of heat on the phosphor
70, the wavelength conversion member containing the phosphor 70 can
be spaced at a certain interval from the light emitting element 10.
On the other hand, in the case where the phosphor is substantially
uniformly distributed in the sealing member, color unevenness of
light can be reduced.
[0049] Also, two or more types of phosphors 70 can be used. For
example, the light emitting device according to this embodiment can
include the light emitting element 10 which emits blue light, the
phosphor which can be excited by the blue light and emit yellow
light together with the phosphor which can be excited by the blue
light and emit red light. In this case, the light emitting device
can emit white light with a good color rendering.
[0050] Also, blue, green, yellow, orange, and red phosphors may be
suitably selected for target spectrum adjustment. Combination of
these phosphors for adjustment can allow fine adjustment of the
color rendering of the light emitting device.
[0051] Examples of phosphors which can emit blue to bluish green
light can be provided by (Ca, Sr, Ba).sub.5(PO.sub.4).sub.3(F, Cl,
Br):Eu, BaMgAl.sub.10O.sub.17:Eu, (Ba, Sr,
Ca).sub.3MgSi.sub.2O.sub.8:Eu, Sr.sub.4Al.sub.14O.sub.25:Eu,
BaSi.sub.7N.sub.10:Eu, (Ba, Sr,
Ca)Al.sub.2Si.sub.3O.sub.4N.sub.4:Eu, and
BaSi.sub.2O.sub.2N.sub.2:Eu, for example.
[0052] Examples of phosphors which can emit green to yellow light
can be provided by silicate phosphors such as (Ca, Sr,
Ba).sub.2SiO.sub.4:Eu and Ca.sub.3Sc.sub.2Si.sub.3O.sub.12:Ce,
chlorosilicate phosphors such as
Ca.sub.8MgSi.sub.4O.sub.16Cl.sub.2-.delta.:Eu
(0.ltoreq..delta..ltoreq.0.5), oxynitride phosphors such as (Ca,
Sr, Ba).sub.3Si.sub.6O.sub.9N.sub.4:Eu, (Ca, Sr,
Ba).sub.3Si.sub.6O.sub.12N.sub.2:Eu, (Ca, Sr,
Ba)Si.sub.2O.sub.2N.sub.2:Eu and
Sr.sub.3Si.sub.13Al.sub.3O.sub.2N.sub.21:Eu, oxynitride phosphors
such as .beta.-SIALON of Si.sub.6-zAl.sub.zO.sub.zN.sub.8-z:Eu
(0<z<4.2), aluminate phosphors activated by Ce such as (Y,
Lu).sub.3(Al, Ga).sub.5O.sub.12:Ce, sulfide phosphors activated by
Eu such as SrGa.sub.2S.sub.4:Eu, oxide phosphors such as
CaSc.sub.2O.sub.4:Ce and SrAl.sub.2O.sub.4:Eu, and nitride
phosphors such as La.sub.3Si.sub.6N.sub.11:Ce, for example.
[0053] Examples of phosphors which can emit yellow to orange light
can be provided by (Sr, Ba, Ca, Mg).sub.2SiO.sub.4:Eu, (Sr, Ca,
Ba).sub.3SiO.sub.5:Eu, (Ca, Sr)Si.sub.2O.sub.2N.sub.2:Eu, (Ca,
Sr).sub.m/2Si.sub.12-m-nAl.sub.m+nN.sub.16-n:Eu, (Sr,
Ca)AlSiN.sub.3:Ce, and (Y, Gd).sub.3(Al, Ga).sub.5O.sub.12:Ce, for
example.
[0054] Examples of phosphors which can emit orange to red light can
be provided by nitride phosphors such as
(Ca.sub.1-xSr.sub.x)AlSiN.sub.3:Eu (0.ltoreq.x.ltoreq.1.0),
(Ca.sub.1-x-ySr.sub.xBa.sub.y).sub.2Si.sub.5N.sub.8:Eu
(0.ltoreq.x.ltoreq.1.0, 0.ltoreq.y.ltoreq.1.0),
SrAlSi.sub.4N.sub.7:Eu and (Ca, Sr)LiAl.sub.3N.sub.4:Eu, halide
phosphors such as K.sub.2(Si.sub.1-x-yGe.sub.xTi.sub.y)F.sub.6:Mn
(0.ltoreq.x.ltoreq.1.0, 0.ltoreq.y.ltoreq.1.0), and sulfide
phosphors such as (Ca, Sr)S:Eu, for example. In the case where
these phosphors for emitting red light are used, components
corresponding to three primary colors can have wide half-value
widths.
[0055] (Sealing Member 50)
[0056] The sealing member 50 is formed of light-transmissive resin
or glass. The recessed part of the light emitting device 100 is
filled with the light-transmissive resin or glass so that the light
emitting element 10 is covered by the sealing member 50. In terms
of ease of production, the sealing member 50 is preferably formed
of light-transmissive resin. In terms of lightfastness, silicone
resin compositions and the like are preferably used as the
light-transmissive resin. However, electrically insulating resin
compositions such as epoxy resin composition, acrylic resin
composition or the like can be also used. Another member can be
suitably included together with the phosphor 70 and the filler
material 80 in the sealing member 50. For example, in addition to
the filler material 80, other light diffusion members can be added
to the sealing member 70. In this case, the directivity from the
light emitting element 10 can be reduced so that the viewing angle
can be increased. Examples of other light diffusion members can be
provided by particles of silica and alumina.
Examples 1-4, and Comparative Example
[0057] Light emitting devices are produced which include neodymium
hydroxide (example 1), and compositions of neodymium aluminate or
neodymium silicate (examples 2 to 4). The following description
describes the measured light emission properties of the light
emitting devices according to the examples 1 to 4 in comparison
with a light emitting device of a comparative example. The produced
light emitting devices according to the examples and the
comparative example are surface mount type light emitting devices
shown in FIG. 2. Each light emitting device includes an LED chip as
the light emitting element 10 having a size of 500 .mu.m.times.290
.mu.m and a light emission peak wavelength of 450 nm. Both
Y.sub.3(Al, Ga).sub.5O.sub.12:Ce and (Sr, Ca)AlSiN.sub.3:Eu are
used as the phosphor 70 in each light emitting device. The material
of the sealing member is a silicone resin. The phosphor, the filler
material, and the silicone resin are mixed at the ratios shown in
Table 2 so that the phosphor and the filler material are
substantially uniformly distributed in the silicone resin. The
silicone resin mixed with the phosphor and the filler material is
dropped into the recessed part of the molded member so as to cover
the light emitting element from the top side of the light emitting
element. After that, the resin is cured.
[0058] The light emitting devices according to the examples 1 to 4
and the comparative example are produced which have the same
structure except that neodymium hydroxide, the compositions of
neodymium aluminate or neodymium silicate, or neodymium oxide is
used as the filler material.
[0059] Table 1 shows the composition of neodymium hydroxide, the
compositions of neodymium aluminate or neodymium silicate, and the
composition of neodymium oxide, and their particle diameters and
reflectance in the examples and the comparative example. The
reflectance of the composition of neodymium hydroxide, the
compositions of neodymium aluminate or neodymium silicate, and the
composition of neodymium oxide in the examples and the comparative
example are reflectance at the wavelengths shown in the rightmost
column of Table 1. Table 2 shows relative luminous fluxes, general
color rendering indices Ra, special color rendering indices R9,
chromaticities x and y, and ratios of the filler materials with
respect to the resin used as the sealing member. The relative
luminous fluxes of the light emitting devices according to the
examples are values where the luminous flux of the light emitting
device of the comparative example, which includes neodymium oxide
(Nd.sub.2O.sub.3) as the filler material, is defined as the
reference luminous flux (100%). The special color rendering indices
R9 indicate redness.
[0060] In addition, FIGS. 8 to 11 show the measured reflection
spectra of filler materials used in the light emitting devices
according to the examples and the comparative example. FIGS. 12 to
15 show the light emission spectra of the light emitting devices
according to the examples and the comparative example. FIGS. 8, 9,
10 and 11 area graphs showing the reflection spectra of the filler
materials used in the examples 1, 2, 3 and 4, respectively,
together with the reflection spectrum of the filler material used
in the comparative example. Also, FIGS. 12, 13, 14 and 15 area
graphs showing the light emission spectra of the light emitting
devices according to the examples 1, 2, 3 and 4, respectively,
together with the light emission spectrum of the light emitting
device of the comparative example.
TABLE-US-00001 TABLE 1 Dm Reflectance Wavelength No. Compositions
(.mu.m) (%) (nm) Ex. 1 Nd(OH).sub.3 1.8 51.8 580 Ex. 2 NdAlO.sub.3
2.0 60.9 585 Ex. 3 Nd.sub.2Si.sub.2O.sub.7, 2.0 60.4 583 Ex. 4
Nd.sub.9.cndot.83((Si,Al)O.sub.4).sub.6O.sub.2 2.0 52.4 585 Comp.
Nd.sub.2O.sub.3 4.9 28.4 599
[0061] As shown in Table 1, the particle diameters of neodymium
hydroxide, and the neodymium aluminate or neodymium silicate
compositions in the examples are about 1.8 to 2.0 .mu.m. As shown
in the reflection spectra of the filler materials shown in FIGS. 8
to 11, the reflection spectrum of each of all of the filler
materials used in the light emitting devices according to the
examples has a low-reflection range (high-absorption range) in the
wavelength range of not shorter than about 575 nm and not longer
than about 605 nm. The reflectance of each filler material in the
low-reflection range is smaller than its reflectance in the
wavelengths longer than the upper limit and shorter than the lower
limit of the low-reflection range. The absorption in the
low-reflection range increases the color rendering of the light
emitting device which includes the filler material used in the
example. The reflectances of the filler materials used in the
examples are not smaller than 50% and not greater than 65% in the
aforementioned wavelength range, and higher than the comparative
example. As a result, the light emitting devices according to the
examples can have higher light emission efficiency than the
comparative example.
TABLE-US-00002 TABLE 2 Resin luminous No. Compositions Ratios (%) x
y Ra R9 flux Ex. 1 Nd(OH).sub.3 4 0.466 0.415 94.0 85.5 131.0 Ex. 2
NdAlO.sub.3 7 0.475 0.429 93.2 89.7 109.2 Ex. 3
Nd.sub.2Si.sub.2O.sub.7, 10 0.473 0.427 91.2 94.5 101.0 Ex. 4
Nd.sub.9..sub.83((Si, Al)O.sub.4).sub.6O.sub.2 7 0.470 0.427 88.6
77.5 103.8 Comp. Nd.sub.2O.sub.3 4 0.470 0.423 88.3 58.9 100.0
[0062] As shown in Table 2, the chromaticities lie around the point
(x, y)=(0.47, 0.42), and the color temperatures are about 2700 K.
As shown in FIGS. 8 to 11, the profiles of the spectra of the
filler materials used in the examples and the comparative example
substantially drop in about 580 to 600 nm. The added amounts of
neodymium hydroxide, and the neodymium aluminate or neodymium
silicate compositions are adjusted so that the intensity ratios of
the drop part around 580 to 600 nm become about 30% with respect to
the highest intensity around 630 nm. The added amounts are 4% to
10%. Ra is around 90, and R9 is 60 to 90.
[0063] Also, as shown in Table 2, it is found that the light
emitting device according to the example 1, which includes
neodymium hydroxide, has a very high relative luminous flux of 131%
where the luminous flux of the light emitting device according to
the comparative example, which includes neodymium oxide, is defined
as 100%. As discussed above, it is concluded that the luminous flux
and the color rendering of the light emitting device can be
improved when neodymium hydroxide, neodymium aluminate, or
neodymium silicate is used as the filler material as compared with
case where the neodymium oxide is used.
First Modified Embodiment
[0064] Although the light emitting device according to the
foregoing embodiment has been described, light emitting devices
according to modified embodiments can be constructed by adding
processes for distributing the phosphor and the filler material in
different parts of the sealing member, or separately positioning
the phosphor and the filler material. Since the production method
of the light emitting device according to the foregoing embodiment
can omit the processes for distributing the phosphor and the filler
material in different parts of the sealing member, or separately
positioning the phosphor and the filler material, the light
emitting device according to the foregoing embodiment can be easily
produced, and the production workability can be improved. From this
viewpoint, it can be said that the foregoing embodiment is better
than the following modified embodiments.
[0065] The sealing member 50 according to a first modified
embodiment includes first and second portions. The first portion
covers the light emitting element 10, and contains the phosphor.
The second portion covers the first portion, and contains the
filler material 80. FIG. 3 is a cross-sectional view showing a
light emitting device 200 according to the first modified
embodiment. The sealing member of the light emitting device 200
shown in FIG. 3 includes the first portion which covers the light
emitting element 10 and contains the phosphor 70, and the second
portion which contains the filler material 80 on or above the first
portion. To form this sealing member 50, the resin material of the
sealing member containing the phosphor can be dropped onto the
light emitting element, and subsequently the resin material
containing the filler material can be dropped. After that, the
resin materials can be cured. According to this process, the
sealing member which includes the aforementioned first and second
portions can be relatively easily formed so that the phosphor and
the filler material can be arranged on or above the light emitting
element 10.
Second Modified Embodiment
[0066] A light emitting device 300 according to the second modified
embodiment shown in FIG. 4, the sealing member is constructed of a
plurality of parts similar to the first modified embodiment. For
example, the parts can be a first portion 72 which the phosphor 70,
and a second portion 82 which contains the filler material 80 on or
above the first portion 72. The first and second portions 72 and 82
are separately provided, and formed in layers so that each of the
layers has a substantially uniform thickness in all directions.
This sealing member containing the first and second portions 72 and
82 can be formed by filling molds, which have shapes corresponding
to the first and second portions 72 and 82, with the resin
materials, which contains the phosphor 70 and the filler material
80, and curing the resin materials corresponding to the first and
second portions 72 and 82, for example.
[0067] It is noted that the boundary between the first portion 72,
which contains the phosphor 70, and the second portion 82, which
contains the filler material 80, is clearly shown in FIG. 4 for
ease of representation in the drawing. However, the present
invention is not limited to this. The first portion containing the
phosphor 70 and the second portion containing the filler material
80 do not necessarily have a clear boundary between them. That is,
no clear boundary may be formed between the first and second
portions. For example, the concentrations of the filler material
and the phosphor may vary in the layer thickness direction.
Third Modified Embodiment
[0068] Although the filler material has been described to be
arranged in proximity to the phosphor and the light emitting
element in the foregoing embodiment, the present invention is not
limited to this. That is, the aforementioned first and second
portions can be spaced at an interval away from each other. For
example, as shown in FIG. 5 (third modified embodiment) or 6
(later-discussed fourth modified embodiment), the phosphor 70 can
be arranged around the periphery of the light emitting element 10,
while a sealing member 50 that includes neither the phosphor 70 nor
the filler material 80 can be arranged between the phosphor 70 and
the filler material 80 so that a second portion 84 or 86 which
contains the filler material 80 can be arranged on or above the
sealing member 50.
[0069] In the first to third modified embodiments where the filler
material is physically spaced away from the phosphor as discussed
above, the filler material can more effectively absorb a part of
color-mixed light of the phosphor and the light emitting element 10
and more effectively reflect the other parts of the color-mixed
light. In other words, in the case where the filler material is not
spaced away from the phosphor, a part of light of the light
emitting element or a part of light of the phosphor may be
extracted from the light emitting device without subjected to the
control of the filler material. Contrary to this, in the case where
the filler material is spaced away from the phosphor so that the
filler material is arranged on the exterior side of the phosphor
with respect to the light emitting element, the light of the light
emitting element and the light of the phosphor can be more
effectively subjected to the control of the filler material.
[0070] In addition, in the case where the filler material 80 is
spaced away from the light emitting element 10, there is an effect
that the filler material 80 can be protected from heat that is
dissipated from the light emitting element 10. Also, as for the
phosphor 70, in addition to the filler material 80, both the filler
material 80 and the phosphor 70 may be spaced away from the light
emitting element 10. For example, the phosphor 70 may be arranged
in a layer of resin under the second portion 84 containing the
filler material 80.
Fourth Modified Embodiment
[0071] The first or second portion can be arranged on the upper
surface of the molded member. For example, in the fourth embodiment
shown in FIG. 6, the second portion 86 containing the filler
material 80 is arranged on the upper surface of the molded member
40, which has the recessed part.
[0072] The shape of the sealing member mixed with the filler
material is not specifically limited. For example, as shown in FIG.
6, the second portion 86 of a light emitting device 500 according
to the fourth modified embodiment has a lens shape of the sealing
member, and contains the filler material 80 which is distributed in
the second portion 86.
Fifth Modified Embodiment
[0073] A light emitting device 600 according to a fifth modified
embodiment shown in FIG. 7 includes a cylindrical covering member
88 which covers the periphery of the light emitting element 10 as
viewed in cross-section. The filler material 80 is mixed in the
covering member 88. In another modified embodiment, the filler
material 80 may be applied on the surface of the covering member.
In the case where the filler material is contained in an
independent member separated from the sealing member that contains
the phosphor, existing light emitting devices can be easily
subjected to control of the filler material according to this
embodiment of the present invention.
[0074] Since the light emitting devices according to the
embodiments of the present invention can have a high color
rendering and a high efficiency, they are of great value in
industry. They can be used not only for a lighting apparatus but
also for a display apparatus (e.g., display and radar), LCD
backlight, and the like.
* * * * *